Ski having tensioning means to change the flexibility of the ski



Aug. 27, 1968 M. F. MUTZHAS 3,398,968

SKI HAVING TENSIONING MEANS TO CHANGE THE FLEXIBILITY OF THE SKI Filed Feb. 21, 1966 4 Sheets-Sheet 1 g- 1968 M. F. MUTZHAS 3,

SKI HAVING TENSIONING' MEANS TO CHANGE THE FLEXIBILITY OF THE SKI Filed Feb. 21, 1966 4 Sheets-Sheet 2 M. F. MUTZHAS 3,398,968

SKI HAVING TENSIONING MEANS TO CHANGE Filed Feb. 21. 1966 THE FLEXIBILITY OF THE SKI 4 Sheets-Sheet 3 Aug. 27, 1968 M. F. MUTZHAS 3,

SKI HAVING TENSIONING MEANS TO CHANGE THE FLEXIBILITY OF THE SKI Filed Feb. 21, 1966 4 Sheets-Sheet 4 SKI HAVING TENSIONING MEANS TO CHANGE THE FLEXIBILITY OF THE SKI Maximilian Friedrich Mutzhas, Wettersteinplatz 3, Munich, Germany Filed Feb. 21, 1966, Ser. No. 529,112 Claims priority, application Germany, Feb. 26, 1965,

19 Claims. (Cl. 280-11.13)

.ABSTRACT OF THE DISCLOSURE A ski comprising a plurality of interconnected layers arranged in superimposed relation, of which an intermediate layer has provided therein a lengthwise extending slot or groove in which is disposed a tension producing means in the form of straps extending from substantially the center portion of the ski toward the outer ends thereof where these ends of the straps are anchored to the ski body while the inner ends of the straps engage or are subjected to the effect of a tensioning member, such as a rotatable cam which upon rotatable adjustments transfers variable thrust forces to said straps for changing the elasticity of the ski body against deflections at right angles to its running surface.

The present invention relates to a ski consisting of one or several superimposed layers, or groups of layers, which are connected with each other and particularly to such a ski in which the relative tension against deflection of the layers or groups of layers disposed above and/or below the neutral horizontal plane is variable for changing the elasticity against deflection along the longitudinal axis at right angles to the running surface of the ski.

The elasticity of a ski against deflection along its longitudinal axis and at right angles with respect to the running surface influences decisively its gliding properties. For a certain body weight, a certain body size, and a certain skiing style of the skier, the most favorable longitudinal elasticity, i.e., the elasticity constant, changes with variations in terrain and the properties of the snow.

In order to be able to change the elasticity properties of a ski, it has been the practice to insert over the length of the ski, tension or compression elements which exert additional tensional or compressional forces in longitudinal direction of the ski either below or above the neutral horizontal plane, and this depending on the strains in the respective layer when the ski is stressed for deflection. It is, for instance, also well known to employ for prevention of flutter effects a tensionor compression-rod system in the ski bindings on the top side of the ski, which system is securely fastened to the ski at the front and rear end, and rests with its middle portion against an interposed spring system. Well known is also the method of inserting tension ropes in grooves between the glide layer and the main layer of the ski, whereby these ropes are secured at the tip and the rear end of the ski but otherwise free for sliding movement in the grooves. In some known forms the tension elements are bands or straps instead of ropes. Moreover, a decrease in the elasticity of the ski has heretofore been obtained by inserting thrust or pressure rods in its neutral fiber, which rods are to effect the flexure qualities by altering the original curvature.

All such known arrangements, however, have their limitation in that they influence the tensions in the ski only at individual points, so that it maintains varying deflection properties over its length. They permit, furthermore, either tension effects only or require, when compression effects are desired, heavy rod systems due to buckling stress in the thrust members. To increase the United States Patent deflection resistance of the ski by action of tension elements, such elements must 'lie in the lower layers of the ski and their insertion there is rather diflicult' and costly.

It is an object of this invention to provide an arrangement for influencing the elastic properties of the ski substantially uniformly over its whole length and without adding substantially to its weight, and without much noticeable appearance at the surface of the ski. This arrangement is simple in construction and can be built into the ski within the facilities of normal ski production. According to this invention, this object is achieved by arranging a tension element outside the neutral horizontal plane and extending it substantially over'the entire length of the ski, whereby this tension element is secured with respect to the ski within the cross-sectional planes of the latter over its entire length.

The tension element referred to may consist of at least one strap having a flat cross-section, and this thrust strap can be slidably embedded in a slot extending lengthwise of the ski in a layer beneath the cover layer. It has been found advisable to insert the thrust strap in a tube having a flat rectangular cross-section and being adhesively secured in the slot. By embedding the thrust element in a slot or a tube directly beneath the cover layer, the greater part of the buckling stress is taken by the ski itself with the result that the elastic properties of the ski are uniformly distributed over its entire length. In particular, when employing the flat tube-type jacket, the torsional properties of the ski are not impaired. Thus, with the proposed means there are achieved more favorable sliding properties of the ski than with conventional arrangements for varying the flexibility of the ski.

In accordance with another object of the invention, one employs materials of dififerent thermal expansion coefficients for the layers outside the neutral horizontal plane, and thereby one produces, depending on these coeflicients, corresponding longitudinal thrust or tension stresses in the respective layer. For proper action, the thermal expansion coeflicients are selected with respect to the crosssections in such a manner that in a range between about -25 C. and 0 C. snow temperature, the ski flexure lies Within the desired limits and becomes softer as the temperature rises, i.e., when the internal tension in the ski decreases.

Still another object of the invention is to provide at least a partial layer in the ski whose bending resistance or flexural strength is variable. This layer, for instance, may consist of a material whose bending resistance decreases with rising temperature in proper relation, so that the ski as a whole is subjected to the desired changes in its elasticity in accordance with temperature variations. Such a layer may also be a strap arrangement, the bending resistance of which is adjustable by mechanical means.

The invention will now be described in greater detail with reference to a few preferred embodiments illustrated in the accompanying drawings, wherein:

FIG. 1 is a side elevation view of a ski provided with an arrangement for changing its elastic properties in accordance with this invention;

FIG. 2 is an enlarged cross-sectional view taken on the line IIII of FIG. 1;

FIG. 3 is a top plan view of a portion of a ski equipped with a tensioning device as it may be employed in the ski shown in FIG. 1; parts of the cover layer are broken away and the cover plate and the actuating knob are omitted;

FIG. 4 is a longitudinal sectional view of a part of the ski and showing a somewhat different tension adjusting device than in FIG. 3.

FIG. 5 is a sectional view taken on the longitudinal axis of a part of a ski and showing a modification of the tensioning device for tensioning only in one direction;

in accordance with the present invention;

FIG. 10-is a cross-sectional view taken on the line X-X of FIG. 9;

FIG. 11 is a cross-sectional view of a ski with an interlayer of material having a greater thermal expansion coefficient than the material of the remaining section;

FIG. 12 isa cross-sectional view taken on the line 'XIIX-H of FIG. 14 and of a ski having an interlayer whose bending resistance can be mechanically adjusted;

. FIG. 13 is a fragmentary plan view of an interlayer as in FIG. 12 and in the position for low bending resistance; and

FIG. 14 is a similar view as in FIG. 13 but showing the interlayer in the position for high bending resistance. The ski 1 with binding 2 illustrated in FIGS. 1 and 2 I comprises, for instance, a number of glued wooden strips, namely a center layer 3, a running layer 4, and a cover layer 5. A slot 6 is milled lengthwise into the upper face of the center layer 3 and a fiat tube 7a of plastics with a low friction coeflicient and having a rectangular crosssection, is adhesively secured therein. Slida'bly mounted in the tube 7a is a thrust strap 7. One thrust strap extends from an anchoring abutment 8 near the tip and another from the rear end of the ski through its whole length and to a tensioning device 10 in front of the binding 2.

The tensioning device, as depicted in FIG. 3, is a single unit for producing thrust effects toward the front end of the ski tip and toward the rear end of the ski by means of four thrust straps 7 slidably embedded in fiat tubes 7a and extending two in spaced parallel relation toward the front end and the two other similarly toward the rear of the ski. The tensioning device itself includes a cam element 17 with cam surfaces 17a extending, as shown, in five steps halfway around its periphery. For self-locking the selected adjustments, the cam steps are composed of plane surfaces. A U-shaped guide plate 12 inserted in the ski slidably supports a number of rectangular blocks 16 which cooperate with the steps 17a of the cam 17. The blocks 16 have secured thereto in spaced parallel relation the straps 7 by screws or the like. Filler blocks 16a are disposed between the straps 7. When the cam element 17 is rotatably adjusted, for example, by means of a knob 25 such as shown in the embodiment of FIG. 4, both sliding blocks 16 will be moved simultaneously and uniformly lengthwise of the ski, and will transmit corresponding thrust forces to the thrust straps 7.

As clearly shown in FIG. 4, the aperture provided for the tensioning device 10 in the cover layer of the ski is closed by a cover plate 5a through which projects the square end portion 19 of a stub shaft 18 on which cam element 17b is fixedly mounted. The cam element 17b is somewhat smaller than the cam element 17 and is engaged by two slidable blocks 16b which have a groove 160 into which projects the ends of the straps 7. The adjusting knob 25 is fastened to the end portion 19 by a setscrew or in any other suitable manner. The knob 25 is provided with a slanting bore 27 in a rib-like top portion 25a. This bore 27 serves for the insertion of the tip portion of a skiing pole to be used as an adjusting lever for the tensioning device. The use of a skiing pole as lever is convenient and its length makes possible considerable exertion of force. The bore 27 which extends entirelyrthrough theknob 25 has the advantage that snow collecting therein will be pushed out backwardly when the tip of the pole is inserted therein. A sealing gasket 29 of some suitable plastics, for instance, of the material known under the name polyurethane, is inserted under the knob 25 and around the shaft end portion 19 of the shaft 18 andis pressed in sealing contact with the cover plate 5awhen tightening theiknob25 thereon. The actuating shaft 18 may be pivoted in an elastic sleeve (not shown) extending through an elongated slot 18a. This sleeve allows for a limited movement of the shaft in longitudinal direction of the thrust straps 7 so that an equalization of thrust forces is possible between the two pairs of straps, one pair to the tip and the other to the heel of the ski, whereby is insured "a uniform tension over the whole length of the ski. Moreover, with such an elastic sleeve, an additional retaining effect on the setting of cam element 17 is introduced, and, on the other hand, snow, dirt or dust is thereby prevented from entering the tensioning device and between the sliding surfaces of thrust straps 7. I

The tension adjusting knob 25 may be provided with a calibration at its lower outer rim, which can be set with respect to an indicator mark on the cover plate 5a to show the degree of elasticity for which the ski is adjusted.

In FIG. 5 is shown a modification of a device for tensioning a tension element in one direction only. In this modification, the guide plate 12' carries a projection 31 provided with a threaded bore 32 slanting in longitudinal direction of the ski. The slide block 16' has a beveled surface at right angles to the axis of the threaded bore 32. A screw spindle 33 threadably engages threaded bore 32 and bears with its lower end against the beveled surface of block 16. The threaded spindle 33 carries a head portion 34 with radial holes 35 into which, for instance, the tip of a skiing pole can be inserted. From the construction illustrated, it will be obvious that by rotating the spindle 33, the slide block 16' will be moved along the guide plate 12. The tensioning device is protected by a cover plate 36; however, it is also possible to extend the cover layer 5 of the ski onto the projection 31.

In FIG. 6 there is shown another modification of the tensioning device in which a threaded spindle 37 disposed lengthwise in a recess in the ski engages with both its ends correspondingly threaded bores 38 in the slidable blocks 16". The spindle 37 carries substantially at its center an enlarged cylindrical portion 39 with radial holes 40 in its periphery, and can be rotated for an adjustment of the blocks 16" mad the attached thrust straps 7 by inserting, for instance, the tip of a skiing pole in the holes 40 for gaining leverage.

The FIGS. 7 and 8 illustrate a different method of ski tensioning. In a filler layer 50 of a polyester are embedded over the whole length of the ski, with a sliding-fit and slidable in longitudinal direction, one or several tensioning elements, for example, a steel wire 52. These tension elements are anchored at their ends 53 and 54 on the upper side of the ski and at their center portions are arranged to come to be near the bottom face of the ski. The effective length of the wire 52 can be shortened by means of a tension device 55 or the like. The ski proper is produced with a flat curvature so that in its finished state it has the lowest desirable arc height. After shortening the effective length of one or several tension elements 52, a correspondingly larger portion of the bending stresses during ski running will be taken up by the one or the several tension elements, i.e., the overall stiffness of the ski will be increased and the elasticity reduced. The manufacture of this type of tensioning means in a ski is rather simple and is effected, for example, in that the wire 52 forming the tension element is first coated with a separating film such as silicon, is then placed in position and cast in by pouring the polyester around it. After this process, the tension element 52 is free over its entire length, except at its ends, for sliding movement in the hardened polyester layer 50. I a I According to the embodiment shown in FIG. 8, it is possible to obtain uniform load distribution between several parallel tension elements 52 by means of a single tensioning device 56 when employing a crossbeam 57 in the form of a balance lever and attaching the ends of the tension elements 52 to this beam 57 which at its center is pivotally attached to the tension device 56. The tension device 56 includes a nut and bolt and can be adjusted for different tensions of elements 52 by a knurled nut 58 projecting with a portion of its periphery through the upper face of the cover plate. I

The FIGS. 9 and illustrate another example of a ski with variable elasticity in accordance with this invention. This ski has an upper cover layer 60 and a lower cover layer 61 of sheet metal such as, for instance, aluminum. At their lateral edges, both layers are folded over and overlap each other telescopically as shown in FIG. 10. The joint may be covered at the outside with an elastic strip (not shown). The space between the top and bottom layers 60 and 61 is filled with a somewhat resilient but relatively inflexible polyester sponge material 62 which, if desired may be provided, with glass fiber reinforcements 63 at predetermined regions.

Within the polyester filling 62 and extending over the entire length of the ski, are arranged tension wires 66 which are threaded alternately from top to bottom, and pass through eyelets 64 fixed to the inner faces of the top and bottom layers 60 and 61. The tension wires 66 extend through a suitable opening in the top layer 60 at the forward end of ski 1 and terminate at a tensioning member 65 secured to the outer surface of cover layer 60. It is possible to employ for each tension wire 66 a separate tensioning member or to use a common unit for more than one wire. The tensioning unit in this case may be in the form of a toggle lever or the like. A single tension wire, slidably guided in its longitudinal direction through tensioning member 65 can be folded back here and extended with both halves to the rear portion of the ski, both halves, of course, running through the eyelets as above explained.

The eyelets 64 are not only staggered in longitudinal direction, as shown in FIG. 9, but are also offset between the top and bottom layers 60 and 61 in transverse direction, as is illustrated in FIG. 10. In this arrangement of the eyelets, the tension wires 66 are also capable of resisting considerable lateral stress components occurring during use of the ski and thus relieve the edges of the overlapping ski cover layers from such stresses.

When tensioning or releasing the tension wires 66 by actuating tensioning lever 65, there occurs a vertical contraction or expansion of the polyester filling 62 and simultaneously a telescopic movement between the overlapping edges of the cover layers, whereby is changed the distance between both layers and therewith the curvature and the elasticity of the ski.

The ski illustrated in cross-section in FIG. 11, comprises a metal housing having a top portion 72 of an inversed U-shaped section and a bottom or running layer 73. The running layer has arranged thereon a layer 75 of a material having a relatively high thermal expansion coefiicient and serving as a tensioning element. The crosssection thereabove consists of a material 76 having a lower thermal expansion coefiicient than that of layer 75. With such layers of material having different thermal expansion coefficients, it is achieved that the layer in the lower portion of the cross-section contracts more than the layer in the upper portion. The result is that the tension over the entire length of the ski is uniformly increased, and this in accordance with the tension change desired,

when the materials are properly selected and arranged tangular tube 82 cast into the upper portion of the ski directly beneath the cover plate andextending over its entire length. The webs 83, formed by the narrow lateral sides of the tube 82 are interrupted at regular intervals by slots 84, which latter considerably reduce the bending resistance of the tube 82. A strap is arranged in the tube 82 with sliding fit and is free to slide therein in longitudinal direction ofthe ski. The strap 85 has lateral notches 86 in similar spacing as the slots 84 in webs 83 of tube 82. I

When, as'shown in FIG. 13, the notches 86 in strap 85 register with the slots 84 in the tube 82, the bending resistance of the combination is relatively low. However, when the strap 85 is slidably adjusted into the position as shown in FIG. 14, the slots 84 in the tube 82 register with the wide portion of the strap 85 between the notches 86, and the decreased bending resistance of the tube 82 produced by the slots therein, will be annulled and the combination of tube 82 and the strap 85 has now a considerably greater stiffness than when in the relative position of these parts, as shown in FIG. 13.

When utilizing a tension assembly, as illustratedin FIG. 12, the stiffness of the ski can be altered in a range between two desirable limit values by shifting the strap 85 into different position with respect to the tube 82. This can be accomplished by means of a conventional adjusting device (not shown) preferably located on the upper face of the ski. By a suitable spacing of the slots 84 in the tube 82 and the notches 86 in the strap 85, it can be achieved that by shifting the strap into a first position, all notches 86 are in alignment with all slots 84, or into a second position, in which every other slot 84 is bridged by a wide portion of strap 85, or finally into a third position in which all slots 84 are bridged by wide portions of the strap 85. In this way it is possible to obtain progressive tension changes in three or even more ste s.

l Vhile the invention is herein described with reference to several preferred embodiments thereof, it will be obvious to those skilled in the art that various changes may be made without departing from the broader aspects of the invention. It is, for instance, feasible that the ski of FIG. 11, be provided with electrical heating elements which are controlled as desired by a thermostat lying on the outside of the ski, or that in the construction of FIGS. 12 to 14, the adjustment in the position of the strap 85 is elfected by a thermostat or another detector sensing the conditions that require a change in the flexibility of the ski. Therefore, it is the aim of the appended claims to cover. all changes falling within the ,true spirit and scope of this invention.

What I claim is:

1. In a ski comprising a plurality of interconnected layers arranged in superposed relation, which when subjected to bending stresses have variable relative tensions with respect to a neutral horizontal plane within the same which changes the elasticity against flexure at right angles to the running surface of the ski; the improvement comprising the arrangement of at least one tension element disposed outside said neutral plane and extending substantially over the entire length of the ski, and means for securing said tension element against displacement at right angles to the longitudinal axis of the ski, said tension element consisting of at least one thrust strap having a crosssection whose dimension in the direction of the width of the ski is a multiple of its height, and wherein said layers include a cover layer and a second layer directly below said cover layer, a lengthwise extending slot in said second layer, said thrust strap slidably arranged in said slot, and a tensioning device for adjusting the lengthwise tension of said thrust strap.

2. A ski according to claim 1, in which a tube of a material with a low friction coefficient is adhesively secured in said lengthwise extending slot and that said thrust strap is slidably disposed in said tubing.

3. A ski according to claim 1, in which said thrust straps have a substantially rectangular cross-section.

4. A ski according to claim 1, including anchoring means located near the front end and near the rear end of the ski to which the ends of said thrust strap are attached.

5. A ski as claimed in claim 1, including a tensioning device having slide blocks to which a plurality of thrust straps are attached.

6. A ski according to claim 5, in which said tensioning device includes a manually adjustable rotatably mounted cam element.

7. .A ski as claimed in claim 1, including a tensioning device having slide blocks to which a plurality of thrust straps are attached, said slide blocks being provided with shoulders and projections having flat surfaces, the end portions of said thrust straps resting flatly on said surfaces and abutting said shoulders.

8. A ski as claimed in claim 1, including a tensioning device having slide blocks to which a plurality of thrust straps are attached, said slide blocks being guided along a guide plate.

9. A ski comprising a plurality of superposed interconnected layers forming the body of the ski, said layers being arranged in two groups, one below and one above a neutral horizontal plane, both groups causing a resultant tension which affects the elasticity controlling the fiexure of the ski at right angles to the running surface of the same and including tension elements in said body for changing said elasticity, and a device for varying the tension of said tension elements, said tension elements comprising at least one thrust strap extending from said device in only one direction to one end of the ski, said device including at least one slide block to which said thrust strap is secured, a guide plate in which said slide block slides and which carries a projection with a threaded bore, a spindle threadably engaging said bore and adapted to bear against said slide block to effect a slidable movement thereof and thereby tensioning said thrust strap.

10. A ski comprising a plurality of superposed interconnected layers forming the body of the ski, said layers being arranged in two groups, one below and one above a neutral horizontal plane, both groups causing a resultant tension which affects the elasticity controlling the flexure of the ski at right angles to the running surface of the same and including tension elements in said body for changing said elasticity, and a device for varying the tension of said tension elements, said tension elements comprising two pairs of thrust straps, one extending from said device toward the front end and the other toward the rear end of the ski, said device comprising a guide member, two blocks slidably arranged in said guide member, one pair of said thrust straps secured to one, the other pair to the other of said slide blocks, said slide blocks having plane faces opposite to the side to which said thrust straps are secured, a cam element interposed between the flat faces of said slide blocks, the cam surface of said cam member being subdivided into a plurality of plane surface steps which, upon rotation of said cam element, successively engage at opposite sides the plane surfaces of said slide blocks.

11. A ski set forth in claim 10, including a manually operable knob for rotatably adjusting said cam element, said knob abutting the upper surface of the ski and having a top portion provided with a bore through there adapted to receive the tip of a skiing pole as an actuating lever.

12. A ski as set forth in claim 11, including a shaft interposed between said cam element and said knob, a sealing gasket disposed around said shaft and between the upper surface of the ski and the bottom of said knob, and fastening means for securing said knob on said shaft seat the latter in sealing contact with the upper surface and adapted to exert pressure on said sealing gasket to of the ski.

13. A ski comprising a plurality of superposed interconnected layers forming the body of the ski, said layers being arranged in two groups, one below and one above a neutral horizontal plane, both groups causing a resultant tension which affects the elastically controlling the flexure of the ski at right angles to the running surface of the same and including tension elements in said body for changing said elasticity, and a device for varying the tension of said tension elements, said tension elements comprising two sets of thrust straps, one set extending from said device toward the front end and the other set toward the rear end of the ski, said device comprising a guide member, two blocks slidably arranged in said guide member, one set of said thrust straps secured to one, the other set to the other one of said blocks, said blocks having flat'faces opposite to the side to which said thrust straps are secured, a cam element having two cam faces arranged diametrically opposite each other, each engaging the plane face of the respective blocks, a shaft carrying said cam member being mounted in said guide member for restricted movement in longitudinal direction of the ski to provide for equalization of tension between the two sets of thrust straps extending one toward the front end and the other toward the rear end of the ski.

14. A ski as set forth in claim 13, in which the means for restricted longitudinal movement of said shaft is formed by a sleeve of elastic material.

15. A ski comprising a plurality of superposed interconnected layers forming the body of the ski, said layers being arranged in two groups, one below and one above a neutral horizontal plane, both groups causing a resultant tension which affects the elasticity controlling the fiexure of the ski at .right angles to the running surface of the same and including tension elements in said body for changing said elasticity, a device for varying the tension of said tension elements, and including a ski binding, and in which said tension elements comprise one thrust strap extending from the front end and another thrust strap extending from the rear end of the ski, both said straps extending into said device which is located near the ski binding.

16. A ski comprising a plurality of superposed interconnected layers forming the body of the ski, said layers being arranged in two groups, one below and one above a neutral horizontal plane, both groups causing a resultant tension which affects the elasticity controlling the flexure of the ski at right angles to the running surface of the same and including tension elements in said body for changing said elasticity, and a device for varying the tension of said tension elements, said tension elements comprising at least two thrust straps arranged in spaced parallel relation and wherein said device includes a single slide block to which both said thrust straps are attached, a cam member for imparting sliding motion to said slide blocks, and actuating means for said cam member.

17. A ski comprising a plurality of superposed interconnected layers forming the body of the ski, said layers being arranged in two groups, one below and one above a neutral horizontal plane, both groups causing a resultant tension which eifects the elasticity controlling the flexure of the ski at right angles to the running surface of the same and including tension elements in said body for changing said elasticity, and a device for varying the tension of said tension elements, said tension elements comprising a plurality of thrust straps slidably arranged for longitudinal straining within the ski body, means for confining said straps against transverse movement in said body, said tensioning device including slide blocks to which said thrust straps are attached, guide members for guiding said slide blocks, and a cam element for actuating said slide blocks for changing the tension of said thrust straps.

18. In a ski comprising a plurality of interconnected layers arranged in superposed relation, which when subjected to bending stresses have variable relative tensions with respect to a neutral horizontal plane within the same which changes the elasticity against fiexure at right angles to the running surface of the ski; the improvement comprising the arrangement of at least one tension element disposed outside said neutral plane and extending substantially over the entire length of the ski, and means for securing said tension element against displacement at right angles to the longitudinal axis of the ski, said layers comprising a top layer and a bottom layer and a somewhat resilient intermediate layer, said layers being curved in longitudinal direction and forming in combination the body of the ski with said neutral horizontal plane disposed within said resilient intermediate layer, and means for altering the distance between the end of said outer layer and therewith the degree of compression in said intermediate layer, said means for altering the distance between the ends of said outer layers comprising a plurality of eyelets fixed to the inner face of said two outer layers over their entire length and staggered alternately between said two layers, a tension wire being slidably embedded in said intermediate layer and threaded through said eyelets in a zigzag path, and means for adjusting the effective length of said wire and therewith the distance between said two outer layers.

19. In a ski comprising a plurality of interconnected laye'rs arranged in su erposed relation, which when subjected to bending stresses have variable relative tensions with respect to a neutral horizontal plane within the same which changes the elasticity against fiexure at right angles to the running surface of the ski; the improvement comprising the arrangement of at least one tension element disposed outside said neutral plane and extending substantially over the entire length of the ski, and means for securing said tension element against displacement at right angles to the longitudinal axis of the ski, said tension element comprising a tube of flat rectangular cross-section having a plurality of slots at predetermined intervals in both its smaller side walls, and a strap slidably inserted in said tube and free to slide in longitudinal direction therein and having notches in both longitudinal edges at the same intervals as the slots in said tube, and means for altering the relative position between said tube and said strap, so that in one position all slots and notches are in alignment, while in another position some slots are in alignment with some notches, and in a third position none of the slots are in alignment with any notches but register with full sections of the strap, whereby the bending resistance of said tension element is varied and the internal tension and therewith the flexibility of the ski be changed.

References Cited UNITED STATES PATENTS 2,188,582 1/1940 Serr 280'11.13 2,918,293 12/1959 Tave 280-11.13 3,300,226 1/1967 Reed 280-1 1.13 3,322,435 5/ 1967 Kirschner 2801 1.13

FOREIGN PATENTS 1,118,857 3/1956 France. 1,269,049 6/ 1961 France. 1,304,880 8/ 1962 France.

185,151 9/ 1936 Switzerland.

BENJAMIN HERSH, Primary Examiner.

MILTON -L. SMITH, Assistant Examiner. 

